This invention relates generally to alarm systems and more particularly to an interface device for connecting an alarm system control panel to a special phone line.
Some residential and commercial alarm systems are connected to a telephone line so that an alarm condition can be transmitted to a monitoring facility and an appropriate response can be initiated. Most present day alarm systems have control panels that are designed to connect to conventional analog telephone lines. Increasingly, special telephone services such as xDSL are installed that carry signals at frequencies higher than those used for normal analog telephone connections. The signals on these non-standard telephone lines may interfere with the operation of analog alarm system control panels.
As used herein, a special telephone line is a telephone line that carries signals other than or in addition to conventional analog telephone signals, and particularly signals that would interfere with the operation of a conventional DACT. Special signals means those signals carried by a special telephone line that would, if not removed, interfere with the operation of an alarm system control panel DACT.
Most alarm system control panels use an industry standard Digital Alarm Communicator Transmitter (DACT) to interface with the telephone line. Standard DACTs were designed prior to the widespread introduction of special phone lines such as xDSL. The signals appearing on these non-standard lines are known to interfere with the proper operation of DACTs and, therefore, with the proper operation of the alarm system control panel. Filters have been developed for connection between a special telephone line and analog devices. Such filters can be connected between the alarm system control panel DACT and a special telephone line for removing special signals that would otherwise interfere with the operation of the DACT. The filters effectively address the problems created by special telephone lines in some premises wiring configurations, but create additional problems in others. When a telephone line splitter is used to connect the incoming telephone circuit to a DSL modem connected to one port and a filter and analog telephone sets connected to another port, an alarm system control panel can be connected between the filter and the telephone sets and operate normally. Similarly, when a combination DSL modem/ splitter is used to provide a network connection and an analog connection, the control panel can be connected in series with the analog telephone sets and connected to the analog connection of the DSL modem/splitter.
Another arrangement creates additional problems, however. Many prewired premises telephone lines are xe2x80x9cdaisy chainedxe2x80x9dfrom one phone outlet to the next. A DSL modem can be connected directly to any phone jack to provide a data connection to a personal computer or the like. Each analog telephone set requires a filter between it and a phone outlet. The alarm panel cannot be connected between one of these filters and a phone because such an arrangement would permit other analog telephone sets connected to other outlets to interrupt the operation of the alarm panel. The alarm panel must be wired ahead of all of the analog telephones. To do so in the daisy chain arrangement, however, would connect the alarm panel to the telephone line ahead of any filtering and, as already discussed, this would create problems with special signals being applied to the control panel DACT, resulting in unreliable operation.
It is an object of this invention to provide apparatus and an arrangement for allowing an alarm system control panel to be effectively connected to a special telephone line in a premises wired in a daisy chain configuration, without rewiring the entire premises.
It is another object of this invention to provide an interface for an alarm system control panel that allows the control panel to be connected to a special telephone line upstream from a plurality of daisy chained house telephones and a DSL modem.
Briefly stated, in accordance with the presently preferred embodiment of the invention, an interface for connecting an alarm system control panel and one or more telephone sets to a special telephone line includes a filter connected in series between the special telephone line and an alarm system control panel for removing special signals from the special telephone line, a controllable switch connected to the filter and the special telephone line for selectively enabling and disabling the filter, and a control circuit connected to the controllable switch for enabling the filter when the alarm system control panels goes off hook.
In accordance with another aspect of the invention, the alarm system control panel includes a port for connecting one or more telephone sets and one or more special devices such as a DSL modem to the telephone line.
In accordance with still another aspect of the invention, the control circuit includes first and second current sensors for sensing current in the connection between the alarm system control panel and the special telephone line on the one hand and current between the alarm system control panel and the one or more telephone sets and one or more special devices on the other hand.
In accordance with still another aspect of the invention, the control circuit is responsive to current flowing from the special telephone line to the control panel and the absence of current flowing from the alarm system control panel to the one or more telephone sets and one or more special devices to enable the filter.
In accordance with a still further aspect of the invention, the current sensors comprise optoisolators.